JP3385995B2 - Overcurrent detection circuit and semiconductor integrated circuit incorporating the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent detection circuit and a semiconductor integrated circuit incorporating the same, and more particularly to a circuit for detecting an overcurrent state of an output transistor having an open drain structure and a semiconductor integrated circuit incorporating the same.

[0002]

2. Description of the Related Art Generally, a semiconductor integrated circuit for driving a solenoid or the like often incorporates an output transistor having an open drain structure. In such a semiconductor integrated circuit, if an external load such as a solenoid fails and is short-circuited, or if the external power source connected to the external load fluctuates abnormally, a large current will flow through the output transistor and destroy it. It may end up. In order to prevent such destruction, a mechanism is required that constantly monitors the amount of current flowing through the output transistor and immediately shuts off the output transistor when it detects that it is an overcurrent. Such a mechanism is an overcurrent detection circuit, and a conventional semiconductor integrated circuit incorporating this mechanism will be described below.

FIG. 7 is a diagram showing a semiconductor integrated circuit 70 disclosed in Japanese Patent Laid-Open No. 2-87817.

[0004] The semiconductor integrated circuit 70, or in response to an input signal supplied to the outside from the input terminal, a drive current is supplied to the 'load connected R _L between the' output terminal 73 an external power source V _B It is a device for controlling whether or not. Whether to supply the drive current to the load R _L ′ is determined by whether the output transistor Q ₇₁ having the open drain configuration is in a conducting state or a non-conducting state, and its control is performed by a logic circuit which receives an input signal. . That is, when the logic circuit outputs a high level signal in response to an input signal, the output transistor Q ₇₁ becomes conductive and a drive current flows through the load R _L ′, and conversely, the logic circuit responds to the input signal. Outputs a low level signal, the output transistor Q ₇₁ becomes non-conductive and cuts off the supply of the drive current to the load R _L ′.

However, as described above, the load R_L Because of '
It becomes a short circuit due to obstacles, and external power supply V_B ′ Is abnormally high
When it becomes a voltage, the output transistor Q₇₁When conducting
An unexpected large current flows in the output transistor Q₇₁
May be destroyed. To prevent this,
The body integrated circuit 70 includes a reference voltage generating circuit 71 and a resistor R. ₇₅
And R₇₆, Multiple diodes D₇₁~ D_n1, Comparator 72
Is provided. Such overcurrent
The detection circuit includes a voltage for the output terminal 73 and a reference for detecting an overcurrent.
Voltage V_r By comparing
Langista Q₇₁It is a circuit for detecting the overcurrent state of.

Reference voltage V _r ′ for overcurrent detection
Refers to the output voltage of the reference voltage generation circuit 71 through resistors R ₇₅ and R
It is obtained by dividing the voltage with a voltage dividing circuit in which ₇₆ and n diodes D _{71 to} D _n1 are connected in series. The reference voltage V _r ′ and the output voltage of the output transistor Q ₇₁ are compared by the comparator 72, and the occurrence of overcurrent is detected by the output transistor Q _71.
When it is detected by the abnormal increase in the output voltage of, the overcurrent detection signal is output from the overcurrent detection terminal 74. The overcurrent detection signal is fed back to the logic circuit and controlled so that the output transistor Q ₇₁ is turned off. As a result, the output transistor Q ₇₁ can be protected from damage due to overcurrent.

Here, a plurality of diodes D₇₁~ D_n7Is
Output transistor Q₇₁Compensate for temperature characteristics of on resistance
For overcurrent detection with good temperature dependence
It can be performed. That is, the reference voltage generation circuit 71
Output voltage V_BG′ Is also used for temperature detection by the temperature detection circuit
Since it is used, the output of the reference voltage generation circuit 71
Voltage V_BGThe temperature dependence of ′ must be small, and
Output voltage V of voltage generation circuit 71_BG′ Output transition to itself
Star Q₇₁Have a temperature characteristic that compensates for the temperature characteristic of
I can't. Therefore, overcurrent with good temperature dependence
Use a series connection of diodes to perform current detection
Output transistor Q₇₁Same temperature characteristics as
Reference voltage V held_r ′ Has no temperature dependence
Output voltage V _BG'Is generated.

[0008]

However, since the reference voltage V _r ′ for overcurrent detection is generated by the voltage dividing circuit in which the diodes D _{71 to} D _n7 and the resistors R ₇₅ and R ₇₆ are connected in series, There is a problem that the set range of the detected value is limited to a low value by the voltage drop of the diode connected in series. For example, when five diodes are used, the reference voltage V _r ′ for overcurrent detection is limited to a voltage that is lower than the output voltage V _BG ′ of the reference voltage generation circuit 71 by 5 steps of the forward voltage of the diode. Will end up. For this reason, the degree of freedom in setting the detection range is low, and in some cases, the temperature characteristic is sacrificed to some extent to obtain the desired reference voltage, or conversely, the reference voltage to some extent is required to obtain the desired temperature characteristic. It will be necessary to shift it more than that.

Therefore, an object of the present invention is to provide an overcurrent detection circuit capable of setting an overcurrent detection value to a desired value while sufficiently compensating for the temperature characteristic of an output transistor, and a semiconductor integrated circuit incorporating the same. It is in.

[0010]

An overcurrent detection circuit according to the present invention detects an overcurrent state of an output transistor by comparing a voltage drop due to the on-resistance of the output transistor with a reference voltage. The first temperature characteristic of the output transistor is a first power supply, a reference voltage generation circuit that outputs a first reference voltage based on the first power supply voltage, and the first temperature characteristic. A constant current source circuit that generates a constant current having a second temperature characteristic based on a reference voltage, a current mirror circuit that uses the constant current having the second temperature characteristic as an input current, and an output of the current mirror circuit And a current-voltage conversion circuit for converting a current into a voltage and outputting a voltage having a temperature characteristic proportional to the second temperature characteristic. And for compensating a temperature characteristic having a reference voltage.

The overcurrent detection circuit according to the present invention is an overcurrent detection circuit for detecting an overcurrent flowing in an output transistor connected between an output terminal and a power supply potential, and a predetermined temperature based on a reference potential. A constant current source circuit that generates a first constant current having characteristics, a current mirror circuit that inputs the first constant current and generates a second constant current based on the first constant current, and a second constant current based on the second constant current A current-voltage conversion circuit that generates a reference voltage and a comparator that compares the reference voltage with the voltage of the output terminal are provided, and the predetermined temperature characteristic is substantially equal to the temperature characteristic of the output transistor. Characterize.

Further, the semiconductor integrated circuit according to the present invention is
A semiconductor including an output transistor connected between an output terminal and a power supply potential, a logic circuit that controls a conduction state of the output transistor based on an input signal, and an overcurrent detection circuit that detects a current flowing through the output transistor. In the integrated circuit, the overcurrent detection circuit includes a constant current source circuit that generates a first constant current having a temperature characteristic substantially equal to the temperature characteristic of the output transistor based on a reference potential, and the first constant current source circuit. A current mirror circuit that inputs a current and generates a second constant current based on the current, a current-voltage conversion circuit that generates a reference voltage based on the second constant current, the reference voltage and the voltage of the output terminal And a comparator for generating a detection signal based on the above, the logic circuit irrespective of the input signal in response to the generation of the detection signal. Characterized by said output transistor non-conductive.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An overcurrent detection circuit and a semiconductor integrated circuit incorporating the same according to an embodiment of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 is a circuit diagram showing an overcurrent detection circuit according to a first embodiment of the present invention, and FIG. 2 is an overall schematic view of a semiconductor integrated circuit 9 incorporating the same. Is.

As shown in FIG. 2, the semiconductor integrated circuit 9 includes
An input terminal 10 and an output terminal 3 are provided, and an output transistor Q ₁ is connected between the output terminal 3 and the ground potential. That is, the output transistor Q ₁ has an open drain configuration, and the external load _RL to be driven is connected between the output terminal 3 which is the drain and the external power supply V _B. Although not particularly limited, the external load R _L is, for example, a solenoid.

The input signal supplied to the input terminal 10 first enters the input buffer 11, and then undergoes a predetermined process in the logic circuit 12. As shown in FIG. 2, the logic circuit 12 is
Since it is driven by the voltage between the V _{cc 1} potential and the ground potential, its output amplitude is the V _{cc 1} level. The output signal of the logic circuit 12 having the V _cc1 level amplitude is applied to the level shift circuit 13 and converted into a signal having the V _cc2 level amplitude. Converted signal thus is applied to the gate electrode of the output transistor Q _1, and controls the conduction and non-conduction of the output transistor Q _1.

Here, although not particularly limited, V _cc1 is 5
V and _Vcc2 is 12V. Also, although not particularly limited, the external power supply V _B is also 12 V, which is the same as V _cc2 . As described above, when the voltage of the external power supply V _B connected to the external load R _L is high, the amplitude of the signal for driving the output transistor Q ₁ is increased by using the level shift circuit 13 to increase the amplitude of the output transistor Q ₁ . ON resistance is sufficiently reduced. Therefore, when the voltage of the external power source V _B is not so high or when the on resistance of the output transistor Q ₁ is sufficiently small, the level shift circuit 13 is not necessary. In this case, the output signal of the logic circuit 12 is output from the output transistor Q _1. It may be applied directly to the gate electrode of Q ₁ .

As shown in FIG. 2, the semiconductor integrated circuit 9 is further provided with an overcurrent detection circuit for detecting whether or not the current flowing through the output transistor Q ₁ is within an allowable range. Details of the overcurrent detection circuit are as shown in FIG. 1, and the reference voltage generation circuit 1, the comparator 2, the constant current source circuit 6, the current mirror circuit 7, and the current-voltage conversion circuit 8 are provided.
Consists of.

The reference voltage generation circuit 1 is a circuit for generating a reference voltage V _BG . As shown in FIG. 2, the reference voltage V _BG is used not only for the overcurrent detection circuit but also for the temperature detection circuit. It is a stable voltage with no dependence. However, the temperature detection circuit is an example of another use of the reference voltage V _BG , and provision of this is not essential in this embodiment. Further, the reference voltage V _BG may be used only in the overcurrent detection circuit.

The constant current source circuit 6 is a circuit for generating a constant current I ₁ based on the reference voltage V _BG , and as shown in FIG. 1, the transistors Q ₂ , Q ₄ and the resistors R ₁ , R ₃ , R ₄
, Operational amplifier 5, and n diodes D for temperature compensation
_{It is} composed of _{1 to} D _n . n diodes D _{1 to} D _n
Is a temperature compensating element for matching the temperature characteristic of the output transistor Q _{1 and} the temperature characteristic of the constant current I ₁ .

The current mirror circuit 7 is a constant current source circuit 6
It is a circuit that receives the constant current I ₁ generated by the above and supplies a constant current I ₂ based on the constant current I ₁ to the current-voltage conversion circuit 8. Therefore, if the dimensions of the transistors Q ₂ and Q ₃ are equal, then I ₁ = I ₂ . However, in the present invention, it is not always necessary to make the dimensions of the transistors Q ₂ and Q ₃ equal.

The current-voltage conversion circuit 8 is a circuit that converts the constant current I ₂ supplied by the current mirror circuit 7 into a reference voltage V _r by means of a resistor R ₂ .

As shown in FIGS. 1 and 2, the reference voltage V _r generated by the current-voltage conversion circuit 8 is applied to the inverting input terminal (-) of the comparator 2 and the voltage appearing at the output terminal 3 is applied to the comparator 2. Are input to the respective non-inverting input terminals (+) of the comparator, and the comparator 2 generates the detection signal 4 based on these voltages. That is, the comparator 2 sets the detection signal 4 to a low level when the voltage appearing at the output terminal 3 is lower than the reference voltage V _r, and sets the detection signal 4 high when the voltage appearing at the output terminal 3 becomes higher than the reference voltage V _r. Level.

The detection signal 4 is, as shown in FIG.
It is supplied to the logic circuit 12.

Next, the operation of the overcurrent detection circuit according to the first embodiment of the present invention will be described in detail. First, the output voltage V _BG of the reference voltage generating circuit 1 is _divided by the resistors R ₃ and R ₄ to obtain the reference potential. Enter the reference potential to the operational amplifier 5, the output of the operational amplifier 5 is input to the gate terminal of the transistor Q _4, and by feeding back the signal of the source terminal of the transistor Q ₄ to the operational amplifier 5, the source potential Try to keep it constant. The diodes D _{1 to} D _n and the resistor R ₁ are connected between the source potential and the ground potential, and a constant current I ₁ flows. This constant current I ₁ is given by the equation (1).

I ₁ = ((R ₄ / (R ₃ + R ₄ )) V _BG −nV _F ) / R ₁ [A] (1) where n is the number of diodes and V _F is the forward direction of the diodes. Voltage. Since the transistors Q ₂ and Q _{3 form} the current mirror circuit 7, the mirror current I ₂ according to the area ratio of these transistors flows through the transistor Q ₃ . When the area ratio of the transistor Q _{3 to} the transistor Q ₂ is m, the mirror current I ₂ is converted into the reference voltage V _r by the resistor R ₂ . Reference voltage V
_r is given by equation (2).

V _r = (mR ₂ / R ₁ ) ((R ₄ / (R ₃ + R ₄ )) V _BG −nV _F ) [V] (2) However, the transistors Q ₂ and Q ₃ are current mirror circuits. In order to work, the following formula must be satisfied.

(R ₃ / (R ₃ + R ₄ )) V _BG <V _BG −V _T [V] (3) The temperature coefficient of the reference voltage V _r is (∂V _r / ∂T) from the equation (2). ) = - a _{(nmR 2 / R 1) (} ∂V F / ∂T) [V / ℃] ... (4). FIG. 3 is a temperature characteristic diagram of the forward voltage V _F of the diode, and the reference voltage V _r has the temperature characteristic of the diode as shown in FIG.

Also, the voltage drop V of the output transistor Q _1
DS is represented by V _DS = I _s × R _on , where the detected current value is I _s, and the temperature coefficient is given by equation (5).

(∂V _DS / ∂T) = I _s (∂R _on / ∂T) [V / ° C.] (5) FIG. 4 is a temperature characteristic diagram of the on-resistance R _on measured for the N-channel MOSFET. Therefore, the voltage drop V _DS of the output transistor Q ₁ has the temperature characteristic of the ON resistance shown in FIG. To perform temperature compensation, output transistor Q ₁
The temperature coefficient of the voltage drop V _{DS and} the temperature coefficient of the reference voltage must be equal. Therefore, the number of steps of the diode may be selected from the equations (4) and (5), and an integer closest to N obtained by the following equation may be selected.

[0031] _{N = - (R 1 I s} / mR 2) (∂R on / ∂T) / (∂V F / ∂T) ... (6) reference voltage parameters in a range that satisfies equation (3) Adjust it.

As described above, the reference voltage V _r is generated by the mirror current I ₂ of the constant current I ₁ having the temperature characteristic of the diode generated by the constant current source circuit 6 for obtaining the constant current and the resistor R ₂ , and thus the reference voltage V _r is generated. The setting range of the voltage V _r can be freely set without being affected by the voltage drop of the diode. Therefore, it is possible to widen the detection current range by adjusting the current mirror ratio and the resistance ratio regardless of the number of diode stages.

When the comparator 2 detects that an overcurrent is flowing through the output transistor Q ₁ based on the reference voltage V _r thus generated and the voltage appearing at the output terminal 3, the comparison is performed as described above. The device 2 sets the detection signal 4 to the high level, and in response thereto, the logic circuit 12 forcibly sets the output thereof to the low level regardless of the input signal.
As a result, the output transistor Q ₁ becomes non-conductive and the current supply to the external load R _L is cut off, so that the output transistor Q ₁ is protected from being destroyed by an overcurrent.

As described above, according to the present embodiment, the setting of the reference voltage V _r is not affected by the voltage drop of the diode which is the temperature compensating element, so that the temperature characteristic of the output transistor Q ₁ is sufficiently compensated. Meanwhile, the overcurrent detection value can be set to a desired value.

Although the reference voltage V _BG is used as the operating voltage of the current mirror circuit 7 in FIG. 1, the present invention is not limited to this, and as shown in FIG.
You may use _cc2 . In this case, the reference voltage V _r
The setting range of can be increased to the maximum near V _cc2 .
However, it is needless to say that the present invention is not limited to these, and other voltages such as V _cc1 and other voltages can be used as the operating voltage of the current mirror circuit 7.

(Second Embodiment) FIG. 6 is a circuit diagram showing an overcurrent detection circuit according to a second embodiment of the present invention.

The overcurrent detection circuit according to the second embodiment shown in FIG. 6 includes a reference voltage generation circuit 1 and a transistor Q.
₁ , bipolar transistors Q ₅ and Q ₆ , and resistor R
₁ and R _2, and a comparator and n diodes D _{1 to} D _n for temperature compensation. The collector potential of the transistor Q ₅ forming the current mirror becomes equal to the base-emitter voltage. Further, since this potential becomes a constant determined only by the physical parameter, the collector potential becomes constant, so that the operational amplifier is unnecessary in this embodiment. Therefore, the current I ₁ flowing through the diode and the resistor is
Becomes a constant current, and a constant current having a temperature characteristic proportional to the temperature characteristic of the diode is mirrored. Since the mirrored current I ₂ has a temperature characteristic proportional to the temperature characteristic of the diode, the reference voltage V _r also has a temperature characteristic. Therefore, it is possible to widen the detection current range by adjusting the current mirror ratio and the resistance ratio regardless of the number of diode stages.

In the present embodiment as well, another voltage may be used as the operating voltage of the current mirror circuit 7.

[0039]

As described above, according to the present invention,
Since the setting of the reference voltage is not affected by the voltage drop of the diode which is the temperature compensation element, the overcurrent detection value can be set to a desired value while sufficiently compensating for the temperature characteristic of the output transistor. That is, the reference voltage can be easily changed by adjusting the number of diode stages, the current mirror ratio, and the resistance ratio.
This has the effect of increasing the degree of freedom in designing the detection current range.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an overcurrent detection circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a semiconductor integrated circuit having an overcurrent detection circuit.

3 is a temperature characteristic diagram of a forward voltage V _F of the diode of FIG.

4 is a temperature characteristic diagram of an on-resistance R _on of the output transistor Q ₁ of FIG.

FIG. 5 is a circuit diagram showing an overcurrent detection circuit according to a modification of the first embodiment of the present invention.

FIG. 6 is a circuit diagram showing an overcurrent detection circuit according to a second embodiment of the present invention.

FIG. 7 is a diagram showing an example of a conventional overcurrent circuit.

[Explanation of symbols]

1, 71 Reference voltage generation circuit 2, 72 Comparator 3, 73 Output terminal 4, 74 Overcurrent detection terminal 5 Operational amplifier 6 Constant current source circuit 7 Current mirror circuit 8 Current-voltage conversion circuit 9, 70 Overcurrent detection circuit Including semiconductor integrated circuit 10 input terminal 11 input buffer 12 logic circuit 13 level shift circuit D _{1 to} D _n , D _{71 to} D _7n diode elements I ₁ , I ₂ constant current Q ₁ , Q ₇₁ output transistors Q _{2 to} Q ₄ MOS transistors Q _5, Q ₆ bipolar transistors R _L, R _L 'external load _{R 1 ~R 4, R 75,} R 76 resistive elements V _BG, V _BG' reference voltage output voltage V _r of the generator, V _r 'reference voltage

Claims (7)

(57) [Claims] 1. An overcurrent detection circuit for detecting an overcurrent state of the output transistor by comparing a voltage drop due to the on-resistance of the output transistor and a reference voltage, wherein the reference voltage is a first power supply. A reference voltage generation circuit that outputs a first reference voltage based on the first power supply voltage, at least one diode, and the first reference voltage
A second temperature based on the voltage and the temperature characteristic of the diode
A reference voltage including a constant current source circuit that generates a constant current having characteristics, a current mirror circuit that uses the constant current as an input current, and a current-voltage conversion circuit that converts the output current of the current mirror circuit into a voltage. By the generating circuit
The output having the second temperature characteristic is output, and the first temperature characteristic of the output transistor is substantially the same as the first temperature characteristic of the reference voltage.
An overcurrent detection circuit, wherein the detection range of the overcurrent detection circuit is adjusted by the current-voltage conversion circuit while compensating with the same second temperature characteristic. 2. The output terminal of the output transistor is a second terminal.
The overcurrent detection circuit according to claim 1, wherein the overcurrent detection circuit is connected to an output terminal having a load connected to the power supply voltage. 3. The constant current source circuit converts the first reference voltage output from the reference voltage generating circuit into a second reference voltage, and the second reference voltage as an input voltage, and an output transistor. It is supplied to the gate, and an operational amplifier to feed back the source potential of the transistor, at least one between the source potential and the ground potential of the transistor
3. The overcurrent detection circuit according to claim 1, further comprising a means for generating a constant current by providing one diode and a resistor in series. 4. The overcurrent detection circuit according to claim 1, wherein the source terminals of the plurality of transistors forming the current mirror circuit are connected to a third power supply voltage. 5. The overcurrent detection circuit according to claim 1, wherein the current mirror circuit includes a PNP transistor. 6. An overcurrent detection circuit for detecting an overcurrent flowing in an output transistor connected between an output terminal and a power supply potential, which is provided between a reference voltage and a ground potential.
Based on at least one diode
A constant current that generates a first constant current having a predetermined temperature characteristic
The source circuit and the first constant current are input, and the second constant is input based on the input.
A current mirror circuit that generates a constant current, a current-voltage conversion circuit that converts the second constant current into a reference voltage, and a comparator that compares the reference voltage with the voltage of the output terminal. An overcurrent detection circuit, wherein the predetermined temperature characteristic is substantially equal to the temperature characteristic of the output transistor, and the reference voltage is adjusted by the current-voltage conversion circuit. 7. An output transistor connected between an output terminal and a power supply potential, a logic circuit for controlling the conduction state of the output transistor based on an input signal, and an overcurrent for detecting an overcurrent flowing through the output transistor. In a semiconductor integrated circuit including a detection circuit, the overcurrent detection circuit,
At least one datum provided between the reference voltage and the ground potential.
An output transistor based on the diode having an ion
A first resistor having a temperature characteristic substantially equal to that of a resistor
Constant current source circuit for generating a first constant current, a current mirror circuit for inputting the first constant current and generating a second constant current based on the first constant current, and setting the second constant current to a desired set value. Na
So as to convert the current-voltage conversion circuit to the reference voltage, and a comparator that compares the reference voltage and the voltage of the output terminal and generates a detection signal based on the comparison voltage, the logic circuit, the detection signal The semiconductor integrated circuit is characterized in that the output transistor is rendered non-conductive in response to the occurrence of the input signal regardless of the input signal.